Electrochemical cells based on nickel/iron in the form of the nickel/iron accumulator (Edison accumulator) have long been known. The electrode reactions in the charging and discharging of an electrochemical element based on nickel/iron can be described by equations (1) and (2):
Charging2Ni(OH)2+2OH−→2NiO(OH)+2H2O+2e−Fe(OH)2+2e−→Fe+2OH−  (1)Discharging2NiO(OH)+2H2O+2e−→2Ni(OH)2+2OH−Fe+2OH−→Fe(OH)2+2e−  (2).The electrolyte used is generally potassium hydroxide solution.
Nickel-iron accumulators are very reliable and have a long life, but they are generally unsuitable as sources for high-intensity pulsed currents. Accumulators of better suitability for the purpose, in the form of rechargeable nickel-metal hydride batteries, are described, for example, in EP 1 011 163 A1. The electrode reactions in the charging and discharging of nickel-metal hydride batteries can be described by equations (3) and (4):
ChargingNi(OH)2+OH−→NiO(OH)+H2O+e−M+H2O+e−→M−H+OH−  (3)DischargingNiO(OH)+H2O+e−→Ni(OH)2+OH−M−H+OH−→M+H2O+e−  (4).Here too, potassium hydroxide solution is frequently used as electrolyte.
The nickel-metal hydride batteries described in EP 1 011 163 A1 are suitable to safeguard volatile memory in data processing units, an application where high currents have to be provided within a very short time.
Energy sources used to safeguard volatile memory in data processing units may also be capacitors, especially what are called double layer capacitors (“super-caps”). One example can be found in DE 20 2004 017 545 U1. Double layer capacitors have the advantage that they can deliver very high pulsed currents very quickly. However, their capacity is limited in accordance with the nature of a capacitor. Furthermore, most double layer capacitors have an organic electrolyte system which can constitute a safety risk in the event of overcharging.
The batteries described in EP 1 011 163 A1 have a much higher capacity than double layer capacitors. However, the relatively high temperatures that prevail in operation in data processing units can easily lead to overcharging. There is generally no safety risk associated therewith. However, the overcharging can lead to a decrease in the life expectation of the batteries.
It could therefore be helpful to provide an energy source that can release pulsed currents of high intensity and attenuates or removes the above-stated disadvantages.